Israel's President Isaac Herzog labelled South Africa's case of genocide against his country as "atrocious and preposterous" on Tuesday, but there was growing international support for the case.

The case is due to be heard at the International Court of Justice (ICJ) on Thursday.

Herzog said there was nothing more atrocious and preposterous" than South Africa's lawsuit, which accuses Israel of genocide against Palestinians in its Gaza offensive. 

"We will be there at the International Court of Justice and will present proudly our case of using self-defence under our most inherent right under international humanitarian law," he added at a press conference. 

But South Africa's high-powered legal team is preparing to argue before the ICJ that no armed attack on a state's territory, "even an attack involving atrocity crimes", can justify the violation of the Genocide Convention. 

The court will focus the hearings on South Africa's call for the court to declare interim measures against Israel, pending the determination of the genocide case against it.

On Tuesday, more than 1 000 progressive international organisations expressed support for South Africa's case, which calls for the immediate halt of military action in Gaza. 

The legal team, led by advocate Adila Hassim SC, will, in oral arguments on Thursday, argue Israel's military invasion of Gaza after the 7 October attack by Hamas in southern Israel went further than self-defence. 

South Africa's main thrust to the court is that Israel's actions "are genocidal in character, as they are committed with the requisite specific intent … to destroy Palestinians in Gaza as a part of the broader Palestinian national, racial and ethnic group". 

Pre-empting Israel's argument of self-defence, South Africa will rely on a report by the UN Fact-Finding Mission on the Gaza Conflict, established in 2009, which contradicted Israel's claim it was acting in self-defence. 

"The Gaza military operations were, according to the Israeli government, thoroughly and extensively planned.

"While the Israeli government has sought to portray its operations as essentially a response to rocket attacks in the exercise of its right to self-defence, the Mission considers the plan to have been directed, at least in part, at a different target: the people of Gaza as a whole," the 2009 report stated. 

The report further noted, "The repeated failure to distinguish between combatants and civilians appears to the Mission to have been the result of deliberate guidance issued to soldiers, as described by some of them, and not the result of occasional lapses."

South Africa's legal team is due to have three hours to argue its case before the court on Thursday after Israel asked for an extra hour, more than the two hours allocated for its defence the day after. 

In addition to seeking the immediate suspension of Israel's military operation in Gaza, South Africa also wants Israel to be directed to prevent "the expulsion and forced displacement" of Palestinians from their homes, as well as their deprivation of "access to adequate food and water", "medical supplies and assistance", and sanitation.

Among other measures, it also asks that Israel must be directed to "take effective measures to prevent the destruction and ensure the preservation of evidence" related to the genocide allegations against it.

At least 23 210 people have been killed in Gaza and 59 167 wounded since the war began, the Gaza Health Ministry said.

Former Deputy Chief Justice Dikgang Moseneke has been nominated by South Africa as an ad hoc judge to hear the case at the ICJ.

Israeli nominated retired Israeli Supreme Court president Justice Aharon Barak as their judge of choice to be part of the ICJ bench. 

He was quoted as saying the Israeli military complied with international humanitarian law, and Hamas' actions on 7 October, which killed 1 200 people, "was close to genocide". 

"It may be proportional to kill five innocent kids in order to target their leader," Barak said in an interview in November, during which he discussed proportionality. 

Despite these comments, South Africa is unlikely to object to Barak's nomination to the ICJ bench. 

A delegation of South African government officials, led by Justice Minister Ronald Lamola, will be present, and will also include the directors-general of the Presidency, the Department of Justice and Department of International Relations and Cooperation. 

In a statement on Tuesday, Lamola said: "We are determined to see the end of the genocide that is currently taking place in Gaza.

"We are most encouraged by leaders of the world who have not blunted their consciousness and have stood on the right side of history by supporting a case that seeks to protect the rights of human beings, regardless of their nationality or ethnicity."

Jeremy Corbyn, the former leader of Britain's main opposition, the Labour Party, is due to attend the case, supporting South Africa. 

On Monday, he told the UK Parliament that its government should support the case at the ICJ. 

"Cannot the government understand the anger around the world when they watch this happening in real-time?

"And why so many people are pleased that the government of South Africa has taken the initiative to go to the international court in order to hold Israel to account for the deaths of so many wholly innocent people in Gaza.

"Can't the government understand that and at least support the South African process?" he said.

The Organisation of Islamic Countries - a 57-member bloc - backed the ICJ case against Israel. 

Meanwhile, White House National Security Council spokesperson John Kirby said the US considered the case "meritless, counterproductive and completely without any basis in fact whatsoever".

Proceedings are expected to begin at 09:00 South African time on Thursday.